1. Field of the Invention
The present invention relates to a semiconductor switch apparatus for radio frequency signals.
2. Description of the Related Art
In a mobile communication apparatus such as a mobile telephone apparatus using radio frequency signals such as GHz microwave signals, semiconductor switch apparatuses are used for switching the operation of an antenna circuit and a receiving and transmitting circuit.
A prior art semiconductor switch apparatus using GaAs FETs is very simple and therefore, can be constructed by one semiconductor chip. That is, since the GaAs FETs serve as passive elements such as resistors and capacitors, bias circuits for the GaAs FETs are unnecessary. Also, since a substrate of the GaAs FETs is made of semi-insulating material having a high resistance, the leakage of radio frequency signals via the substrate can be suppressed. This will be explained later in detail.
In the above-described prior art semiconductor switch apparatus using GaAs FETs, however, since GaAs substrates are expensive, the manufacturing cost is very high.
In another prior art semiconductor switch apparatus using silicon MOS transistors, in order to suppress the leakage of radio frequency signals, a silicon-on-insulator (SOI) configuration is adopted (see: JP-A-2000-294786) or a resistor is inserted between the back gate of each of the MOS transistors and a ground terminal (see: U.S. Pat. No. 6,094,088). This also will be explained later in detail.
In the above-described prior art semiconductor switch apparatus using silicon MOS transistors, although the manufacturing cost can be low, suppression of the leakage of radio frequency signals is still insufficient, which also will be explained later in detail.
It is an object of the present invention to provide a semiconductor switch apparatus using silicon MOS transistors capable of further decreasing the transmission loss of radio frequency signals.
According to the present invention, in a semiconductor switch apparatus including an input terminal, an output terminal, an AC ground terminal, a DC ground terminal, at least one series MOS transistor connected between the input terminal and the output terminal, and at least one shunt MOS transistor connected between one of the input terminal and the output terminal and the AC ground terminal, the series MOS transistor is formed within a first region of a semiconductor layer on an SOI configuration surrounded by a first trench insulating layer, and the shunt MOS transistor is formed within a second region of the semiconductor layer surrounded by a second trench insulating layer.
Thus, the leakage of radio frequency signals from the series MOS transistor to the shunt MOS transistor can be suppressed by the trench insulating layers.